1. FIELD OF THE INVENTION
The present invention relates to an image forming apparatus, particularly an electrophotographic copying apparatus, comprising a sheet re-feed mechanism for feeding a copy sheet having one side formed with an image by an image forming section to the image forming section again, and a mechanism for detecting the size of the sheet having one side formed with the image and forcibly discharging the sheet when the sheet is unfit for transport by the sheet re-feed mechanism.
2. DESCRIPTION OF THE PRIOR ART
This type of copying apparatus is known from Japanese Patent Publication Kokai No. 62-10667, for example. The apparatus disclosed in this publication checks the size of a copy sheet fed thereto to find out if the sheet is fit for transport conditions of the sheet re-feed mechanism. When the sheet is judged unfit, the sheet is delivered to a discharge section after having one side thereof formed with a copy image instead of being fed to the re-feed mechanism. According to this construction, even if a duplex copying operation is commenced with a sheet having a size unfit for the re-feed mechanism, such a sheet is discharged outwardly through the discharge section after the sheet is formed with an image on one side thereof. Consequently, there is no possibility of a transport failure in a re-feed transport path due to the unfit copy sheet.
However, since the sheet rejected as unfit for the duplex copying is discharged through the discharge section to be stored on a tray, for example, the operator could inadvertently regard the sheet as having come through the duplex copying process. Particularly in carrying out a duplex copying operation by successively feeding copy sheets of different sizes, it is necessary to watch the action of the copying apparatus till completion of the copying operation or to pick up the discharged sheets to confirm that copies have been taken on their back faces. Furthermore, a serious problem may arise when a sorter or a finisher or autostapler is connected to the discharge section of the apparatus. The problem arises from the fact that the sheets, whether duplexed or rejected as unfit, are all delivered alike through the discharged section to the sorter or the finisher.